We have demonstrated that the low density lipoproteins (LDL) exist in two structurally different forms. LDL of d is lesser than 1.019 g/ml exist as association complexes of LP-B and LP-C families, whereas LDL of d is greater than 1.019 g/ml occur as separate entities of LP-B, LP-C and LP-A. The composition and structure of associated complexes of LP-B and LP-C from normal and hyperlipoproteinemic (Types II, III and V) subjects will be studied by physical, chemical and enzymatic methods. The enzymatic studies will be carried out with purified lipoprotein lipases and with post-heparin plasma in the presence and absence of an inhibitor of lecithin:cholesterol acyl-transferase. The hydrolysis products will be isolated ultracentrifugally by equilibrium banding. The free forms of LP-A, LP-B, and LP-C families will be separated by column chromatography and characterized by physical and chemical parameters. The characteristics will then be compared with those of lipoprotein families from naturally occurring LDL2 and HDL. This comparative study will provide a new information not only about the structural composition but also about the metabolic fate of association complexes occurring in the VLDL and LDL density ranges. One of the major initial goals of the proposed studyon the characterization of the protein moiety(ies) of LDL2 (d 1.030-1.050 g/ml) or purified LP-B will be explore and define the most suitable conditions for a complete solubilization of proteins. These studies will include a systematic exploration of various reagents for reduction and blocking of disulfide linkages as well as the effect of solvents on the peptide linkages. The solubilized protein(s) will be fractionated by preparative polyacrylamide gel electrophoresis or by isotachophoresis. The isolated polypeptides will be characterized by the usual physical, chemical and immunological methods. Specific antibodies and immunoadsorbers to each polypeptide will be prepared for isolating and quantifying the corresponding lipoproteins in normal and hyperlipoproteinemic subjects. In case of hypercholesterolemic partients, the ApoB and/or its constitutive polypeptides will be isolated, quantified and carefully scrutinized for any possible physical, chemical or immunological characteristics different from those of the corresponsing polypeptides from normal subjects.